Emit the enum discriminant separately for the Encodable macro

1 files changed, 30 insertions, 17 deletions

diff --git a/compiler/rustc_macros/src/serialize.rs b/compiler/rustc_macros/src/serialize.rs
index 82e6972d027..8d017d149f6 100644
--- a/compiler/rustc_macros/src/serialize.rs
+++ b/compiler/rustc_macros/src/serialize.rs
@@ -42,6 +42,12 @@ fn decodable_body(
     }
     let ty_name = s.ast().ident.to_string();
     let decode_body = match s.variants() {
+        [] => {
+            let message = format!("`{}` has no variants to decode", ty_name);
+            quote! {
+                panic!(#message)
+            }
+        }
         [vi] => vi.construct(|field, _index| decode_field(field)),
         variants => {
             let match_inner: TokenStream = variants
@@ -139,6 +145,11 @@ fn encodable_body(
     });
 
     let encode_body = match s.variants() {
+        [] => {
+            quote! {
+                match *self {}
+            }
+        }
         [_] => {
             let encode_inner = s.each_variant(|vi| {
                 vi.bindings()
@@ -160,6 +171,23 @@ fn encodable_body(
             }
         }
         _ => {
+            let disc = {
+                let mut variant_idx = 0usize;
+                let encode_inner = s.each_variant(|_| {
+                    let result = quote! {
+                        #variant_idx
+                    };
+                    variant_idx += 1;
+                    result
+                });
+                quote! {
+                    let disc = match *self {
+                        #encode_inner
+                    };
+                    ::rustc_serialize::Encoder::emit_usize(__encoder, disc);
+                }
+            };
+
             let mut variant_idx = 0usize;
             let encode_inner = s.each_variant(|vi| {
                 let encode_fields: TokenStream = vi
@@ -176,26 +204,11 @@ fn encodable_body(
                         result
                     })
                     .collect();
-
-                let result = if !vi.bindings().is_empty() {
-                    quote! {
-                        ::rustc_serialize::Encoder::emit_enum_variant(
-                            __encoder,
-                            #variant_idx,
-                            |__encoder| { #encode_fields }
-                        )
-                    }
-                } else {
-                    quote! {
-                        ::rustc_serialize::Encoder::emit_fieldless_enum_variant::<#variant_idx>(
-                            __encoder,
-                        )
-                    }
-                };
                 variant_idx += 1;
-                result
+                encode_fields
             });
             quote! {
+                #disc
                 match *self {
                     #encode_inner
                 }